(a) Field of the Invention
This invention relates to fillers having chemical compositions suitable for those for the fabrication of noise insulating materials and to noise insulating materials formed by blending said fillers with synthetic resin binders by making use of the characteristics of the fillers.
(b) Description of the Prior Art
There have been known to date a variety of noise insulating materials for the prevention of external noise from entering and of sound from emitting outside or sound absorbing materials for weakening the reflection of sound.
These noise insulating materials are processed into sheets and applied or allowed to adhere on the floors or walls of automobiles, rail road cars and buildings or are widely used for the fabrication of composite materials by sticking them together with steel plates, nonwoven fabrics, concrete panels or wood plates. In order to enhance noise insulating effects of these composite materials, it is desirable to fill a filler of high density in as large an amount as possible in a unit weight of a resin.
A noise insulating material with high noise insulating effects requires blending of a greater proportion of a filler having a large specific weight with a binding material of superb processibility, according to the following mass law of sound insulation: EQU TL=a.times.log mf+b
wherein TL is a transmission loss (dB), m is a surface density (kg/m.sup.2), f is a frequency (Hz) and "a" and "b" are individually a constant.
However, fillers, when used for the fabrication of noise insulating materials, can not be filled in binders in large amounts and also can not impart flexibility to the noise insulating materials, if they fail to obtain proper combination with binders. In addition, such problems are raised that upon molding and processing the blended materials what is called a plate-out phenomenon occurs seriously and the surface finish of the products is thereby degraded.
In this connection, a sound proof material has recently been proposed, in which a vinyl chloride resin containing a plasticizer is combined and blended with iron oxides by produced in the steel making process (Japanese Patent Laid-Open No. 34064/1982). In this disclosure, it is emphasized that the iron oxides are excellent in adhesive property with vinyl chloride resins. The oxide-base filler has the following composition and hence contains a lot of CaO.
______________________________________ CaO 50 wt. % SiO.sub.2 14 wt. % FeO & Fe.sub.2 O.sub.3 23 wt. % MgO 7 wt. % MnO 5 wt. % ______________________________________
However, the sound proof material is poorly released from the surface of roll upon its fabrication and also takes prolonged period of time for gelation so that the mechanical properties of the resulting sheets are not deemed satisfactory.
Currently known noise insulating materials employ, as a binder, natural rubber, synthetic rubber, rubber adhesives, polyethylene, polypropylene, polyvinyl chloride, synthetic resin adhesives and asphalt and, as a filler, lead powder, lead compounds, iron powder, iron oxide slag and barytes (barium sulfate), all of which have large specific gravities.
Lead powder and lead compounds are favorable in view of their large specific gravities, but they are expensive and, upon combustion, are liable to evolve toxic dust gases which contain lead oxides. Iron powder is disadvantageous in that it produces rush and thus deteriorates the appearance of the product significantly. Iron oxide slag is inexpensive, but it contains calcium oxide in considerable amounts so that its specific gravity is low as compared with those of the foregoings. Further, iron oxide slag involves problems in that when kneaded into a thermoplastic resin, it adheres to the surface of roll seriously and thus is deficient in processibility.
There have been known to date many noise insulating materials which are fabricated by mixing inorganic powder in a resin and then molding the resultant resin composition. For example, Japanese Patent Publication No. 25375/1983 discloses a resin composition obtained by mixing powder of iron or an iron compound in a mixture of a vinyl chloride resin and a methacrylic resin. Japanese Patent Laid-Open No. 62361/1977 discloses to incorporate a filler, the specific gravity of which is 4 or higher, in the abovedescribed combination of the resins and teaches that the resultant composition has excellent mechanical strength and moldability.
In addition, Japanese Patent Publication No. 21052/1980 discloses a noise insulating material, which makes combined use of an ethylene-vinyl acetate copolymer, especially, an ethylene-vinyl acetate copolymer containing 10-28 wt. % of vinyl acetate and an ethylene-propylene base synthetic rubber, and also teaches its good moldability.
As noise insulating materials imparted with flame retardancy in addition to noise insulating property and flexibility. reference may be had to Japanese Patent Publication No. 32951/1982 and Japanese Patent Laid-Open Nos. 127254/1985 and 127341/1985 which disclose noise insulating materials composed of a PVC-base resin in combination with Sb.sub.2 O.sub.3, tricresyl phosphate and chlorinated paraffin respectively.
Recently, we have also proposed a filler composed of iron oxide and silicon oxide as essential components and also containing basic components such as CaO and MgO in amounts limited below their respective prescribed levels, as well as a noise insulating material obtained by kneading the filler with a vinyl chloride resin and molding the resultant resin composition (Japanese Patent Laid-Open Nos. 56732/1986 and 33887/1987). The present invention relates to an improvement to the above filler and features chemical bonding between iron oxide and silicon oxide.
Further, for noise insulating materials to be used as building materials for interior finish of buildings and hotels, it is important to have sufficient fire protective abilities, or in other words, to be fire retardant and hard to evolve toxic gases and black smoke when a fire takes place.